Self-laying track-type vehicles utilize endless loop track assemblies to support and propel the vehicle. The track assembly is typically driven by a toothed sprocket, supported by a plurality of roller wheels, and guided and reversed by one or more large idler wheels. In order to operate effectively, the endless loop track assembly must be tensioned to a specific force. This tension force must be maintained within optimum limits to prolong the useful life of the track assembly.
If the tension force on the track assembly is lower than optimum, the track becomes slack and sags excessively between the drive sprocket and the idler wheel. Such excess slack produces accelerated wear of the track and associated components and generates undesirable noise levels. Excess slack can also cause the track to become disengaged from the drive sprocket. Higher than optimum track tension force produces a tight track which is also detrimental to long track life. An excessively tight track also produces accelerated wear and can cause fracture of the track and related components.
Conventional track adjusting mechanisms and procedures require the machine operator, or a separate maintenance person, to manually measure the track sag and then manually adjust the sag accordingly. Such procedures generally require removal of a cover plate to gain access to the track adjusting mechanism. The adjusting mechanism is conventionally a small track adjusting fluid cylinder, into which a non-compressible fluid is applied by a manually operated pump. Proper track tensioning by this procedure often requires several track measurements and fluid applications. Should the track inadvertently become over tightened by this process, a separate procedure is necessary to drain off some of the excess pressure in the track adjusting fluid cylinder.
Because of the time and effort required to properly adjust the track using the above noted procedures, track adjustment is often neglected. The working environments and inclement weather often make the track adjustment task an unpleasant one, which also promotes neglect of the procedure.
One type of track tensioning apparatus, which does not require the manual manipulations set forth above, is disclosed in U.S. Pat. No. 4,681,376 issued July 21, 1987, to Peter Riml. The apparatus in this patent includes two fluid cylinders interconnected by a fluid passage with a floating piston positioned in the rear fluid cylinder. The piston divides the rear cylinder into two chambers, and a source of fluid pressure is connected to the rear chamber. The source of fluid pressure includes a control valve, a plurality of fluid conduits, and a plurality of check and throttle valves. The floating piston has a spring loaded check valve which opens when pressurized fluid is applied to the chamber behind the piston. Pressurized fluid flows through the floating piston into the forward chamber and into the forward fluid cylinder. Because of a differential pressure within the rear cylinder, the floating piston is forced to move toward the forward cylinder and displaces a track chain tensioning piston within the forward cylinder in order to tension the track chain. Subsequent interruption of the pressurized fluid to the floating piston, and reward movement of the chain tensioning piston relaxes the track chain to its adjusted condition. Although this apparatus would appear to function satisfactorily to set a desired tension in a track assembly, it includes a rather complex hydraulic circuit having a large number of check valves, throttle valves and fluid lines.
Another type of track tensioning apparatus for hydraulically tensioning the chain of a tracklaying vehicle is disclosed in U.S. Pat. No. 3,647,270 issued Mar. 7, 1972, to Ernst Althans. This apparatus utilizes a hydraulic system, including a fluid cylinder and accumulator, to tension the chain and also to absorb recoil of the idler guide wheel. Besides the fluid accumulator, the hydraulic system includes a pump, a plurality of check valves and pressure limiting valves, and a plurality of inter-connected fluid lines. Initial recoil forces are absorbed by the hydraulic system and subsequent higher recoil forces are absorbed by a pair of springs. Although this apparatus would appear to tension the chain to some desired tensioning pressure, it does not provide for a controlled slack in the chain. This system is also complex and includes several hydraulic components.
The present invention is directed to overcoming one or more of the problems as set forth above.